Embodiments of the invention relate to a thin film transistor liquid crystal display (TFT-LCD) array substrate and a manufacturing method thereof.
Thin film transistor liquid crystal displays (TFT-LCDs) have the advantages of small volume, low energy consumption, low radiation, and etc., and thus prevail in the flat panel display market. A liquid crystal panel is one of the most important components in one TFT-LCD and comprises an array substrate and a color filter substrate, which are assembled together with a liquid crystal layer disposed therebetween. At present, the array substrate is prepared by forming structural patterns by a series of patterning processes. One structural pattern layer can be formed by one patterning process. The array substrate and the manufacture process thereof are critical to the properties, yield and price of the TFT-LCD. In order to effectively decrease the price and increase the yield, the process of manufacturing the TFT-LCD array substrate was gradually simplified. Specifically, the process of manufacturing the array substrate has been developed from a 7-mask process to a 4-mask process by using a half-tone or gray-tone mask.
In a conventional TFT-LCD, a black matrix for blocking leakage light may be provided on the color filter substrate. The black matrix is typically made of opaque metal film of chromium (Cr). Since the metal film of Cr has a high reflectivity to light, the light from backlight can be reflected by the metal film of Cr when it is irradiated on the color filter substrate, and a portion of the reflected light is then irradiated on the semiconductor layer of the TFT channel region. The semiconductor layer is formed of photosensitive material, thus leakage current is generated when the semiconductor layer is irradiated by the reflected light. Because of such leakage current, the turn-off current Ioff is increased so that the retention period of the pixel charges is decreased. Therefore, the gray level change is adversely influenced, and to a severe degree, flickers occur in the display image.
According to the formula of calculating storage capacitance, the storage capacitance per unit area is inversely proportional to the gap between two plates. That is, the larger the gap is, the smaller the storage capacitance per unit area is. In the conventional TFT-LCD, the gate line or the common electrode line in the same layer as the gate line is used as one plate of the storage capacitor, and the pixel electrode formed on the passivation layer is used as the other plate of the storage capacitor, and the gap between two plates of the storage capacitor equals to the sum of the thicknesses of the gate insulating layer and the passivation layer and thus is relatively large. Therefore, the storage capacitance per unit area in the conventional TFT-LCD is relatively small.